Communication via Internet messages is widely used today, and may be performed between computer terminals, e.g. personal computers or PDAs, connected to the Internet over wireless or wire-lined connections. A mobile terminal, e.g. a cellular telephone connected to a wireless radio access network, may also be capable of sending and receiving e-mails to and from another mobile terminal or a computer terminal connected to the Internet.
The commonly used SMTP (Simple Mail Transfer Protocol) provides a reliable transport of Internet messages, of any size, between an SMTP-client, i.e. an Internet message sender, and an SMTP-server, i.e. an Internet message receiver, typically by means of the packet-switched and connection oriented TCP (Transmission Control Protocol), and any mobile terminal or computer capable of e-mail communication can be arranged to function as an SMTP-client, as well as an SMTP-server.
An Internet message, i.e. an e-mail message, comprises a set of headers containing information regarding the sender, the intended recipient or recipients, and the subject of the message, while the message itself is contained in a body appended to the headers. An SMTP/TCP Internet message is further prepended by an envelope, which assists in the routing of the message through a set of intermediate nodes, enabling a so-called hop-by-hop-delivery of the message. Each sender makes a routing lookup and forwards the message to the next-hop server, which repeats the process until the message is delivered to its intended recipients, and on originating sender may be arranged to by-pass the routing step and forward all messages to the same next-hop server, which performs the necessary routing for the onward transport of the message.
The sender and the recipient/s/ of an Internet message are commonly referred to as MUAs (Message User Agents), and may be e.g. a personal computer terminal, and at least some of the intermediate nodes are commonly referred to as MTAs (Message Transfer Agents) e.g. a server. Each server acting as MTA in a SMTP/TCP hop-by-hop delivery of an Internet message is capable of functioning both as an SMTP-client and an SMTP-server for a transported message, and will function as an SMTP-server when receiving an Internet message from a MUA or from another MTA, and function as an SMTP-client when forwarding the Internet message to a second MTA. A MUA is capable of functioning as an SMTP-client when transmitting an e-mail to an MTA.
The latency, or delay, of a connection between two nodes defines the time it takes for a data packet to be transported between the nodes, and a high latency connection induces a comparatively longer delay, or latency, in the data packet transport than a low latency connection. A wireless radio access network, e.g. according to the GPRS (Global Packet Radio Service)/GSM (Global System for Mobile communications) or a 3G/UTRAN (Universal Mobile Telecommunications Systems Terrestrial Radio Access Network) is regarded a high latency network, and the latency between a mobile terminal and a server is approximately 0.5-1.3 second, while a wired connection normally induces a smaller delay and is regarded a low latency connection. Thus, the above-described wireless terrestrial links, as well as interplanetary links, are examples of high latency connections.
The TCP (Transport Control Protocol) is a connection-oriented protocol, providing a reliable transmission of data in an IP environment, and the SMTP/TCP is commonly used in the transport of e-mail messages. The TCP provides stream data transfer, reliability, efficient flow control, full-duplex operation, and multiplexing. The stream data transfer of the TCP delivers an unstructured stream of bytes, and the applications or application layer programs do not have to pack the data for the transmission in a packet data network. Further, the TCP offers reliability by providing end-to-end packet delivery by sequencing bytes with an acknowledgment number that indicates to the source the next byte the destination expects to receive, and any bytes not acknowledged within a specified time interval are retransmitted. The reliability mechanism of TCP is capable of handling lost, delayed, duplicated, or misread packets, wherein a time-out mechanism detects lost packets and request retransmission. The TCP offers efficient flow control, and the full-duplex operation allows the TCP to perform transmission and reception simultaneously. Thus, the TCP enables a very reliable communication of e-mail messages of any size over the Internet.
However, the reliable SMTP/TCP transport of an e-mail between two nodes requires several protocol exchanges, i.e. round-trips, between the STMP-client and the STMP-server, involving an IP packet transmission from the SMTP-client to the SMTP-server, followed by an IP packet transmission in the opposite direction, from the SMTP-server to the SMTP-client, e.g. an acknowledgement or a reply. Since each transmission in any direction induces a latency, which is added to the total transport time of the e-mail, a SMTP/TCP e-mail transport over a high latency connection will be comparatively slow. Consequently, SMTP/TCP transport of an Internet message over a high latency connection, e.g. in a wireless radio access network, will result in a comparatively long overall transmission time between the sender and the recipient of the Internet message.
Thus, a major drawback with the prior art SMTP/TCP is the high number of round trips required between the client and the server, which increases the overall transmission time of an Internet message, especially over high latency connections, such as in a wireless radio access network.
Therefore, an aim of one or more aspects the present invention is to alleviate the problems described above relating to the SMTP/TCP e-mail transport over high latency connections, and to achieve a lower overall transmission time between the sender and the recipient of an e-mail message, which is particularly advantageous in wireless radio access networks.